Popliteal Nerve Block Sciatic Nerve Block in Popliteal Region

The sciatic nerve is a bundle consisting of the tibial and common peroneal nerves contained in an epineural sheath. A popliteal nerve block will block components of the sciatic nerve (tibial and common peroneal) at the level of the popliteal fossa where the two branches typically diverge. The common peroneal nerve gives sensory innervation to the inferior portion of the knee joint and lateral and posterior portion of the upper calf. The tibial nerve is a branch of the sciatic nerve and provides sensation to the posterior portion of the calf, the medial plantar surface, and heel of the foot. The tibial nerve at the knee lies just below the popliteal fossa and runs between the two heads of the gastrocnemius muscle and then passes deep to the soleus muscle. It divides into the lateral and medial plantar nerves as it turns medially between the Achilles tendon and medial malleolus. Dermatome distribution of the lower extremity innervated by the popliteal nerve block is indicated in Table 20.11.

Table 20.11 Popliteal nerve innervation to the lower extremity.

Motor

Sensory

Branches to the knee joint (common peroneal)

Cutaneous branches that form the sural nerve

Superficial and deep peroneal nerves (terminal branches

of the common peroneal)

Medial and lateral plantar nerves (terminal branches of

Collateral branches of the tibial nerve give rise to

the tibial nerve)

cutaneous sural nerves

Muscular branches to the calf and articular branches to

the ankle (tibial nerve)

As primary anesthetic and/or postoperative pain management with or without a continuous catheter.

Clinical Uses Surgical

• Foot and ankle surgery (sensory on the medial part of the foot and ankle innervated by the saphenous nerve)

Surface Anatomy and Landmarks Landmarks

Popliteal fossa crease, tendons of biceps femoris muscle, and tendons of semitendinosus and semimembranosus muscles (Fig. 20.10). Patient is placed in prone position with both feet

Figure 20.10 Landmarks for the intertendinous approach of the popliteal block. Sciatic nerve is positioned between the tendons of the biceps femoris (BF) muscle laterally (1) and the semitendi-nosus/semimebranosus (ST/SM) muscle medially (2). The needle insertion site (X) is marked lateral to the midline between BF and ST/SM muscle tendons and approximately 7-10 cm cephalad to the popliteal crease.

Figure 20.10 Landmarks for the intertendinous approach of the popliteal block. Sciatic nerve is positioned between the tendons of the biceps femoris (BF) muscle laterally (1) and the semitendi-nosus/semimebranosus (ST/SM) muscle medially (2). The needle insertion site (X) is marked lateral to the midline between BF and ST/SM muscle tendons and approximately 7-10 cm cephalad to the popliteal crease.

extending, to the ankles, beyond the block table. Anatomical landmarks of the biceps femoris tendon (laterally), semimembranosus tendon (medially), and semitendinosus tendon (medially) can be accentuated by having the patient flex the leg at the knee. The needle insertion sight is marked 7-10 cm above the popliteal fossa crease and slightly lateral to the midpoint between the medial and lateral tendon surface landmarks. Antiseptic solution cleanses the skin followed by subcutaneous local anesthetic infiltration. The short beveled insulated needle is attached to a nerve stimulator set at 1.0 mA and inserted perpendicular through the skin wheal or at a 45-60° angle to the skin and aimed cephalad toward the ipsilateral shoulder. The goal is consistent stimulation of the either common peroneal or tibial nerves (toes or foot twitch) as the current is decreased to between 0.2 and 0.5 mA. Correct needle placement will achieve a foot twitch ofeither dorsiflexion or eversion (common peroneal nerve) or plantar flexion and/or inversion (tibial nerve) at the ankle. After negative aspiration for blood the local anesthetic is injected with frequent aspiration (every 3-5 cc) to check for blood.

Alternative approaches to individually block each the tibial (A) and common peroneal (B) nerves are described as follows:

A. Patient is placed in the prone position, and the apex of the triangle at the convergence of semitendinosus and the biceps femoris tendons/muscles is identified. The base of the triangle is the skin crease of the knee. In an aseptic fashion at the center of the apex a 22 g 1.5 in. needle is inserted perpendicularly until a paresthesia in the distribution of the tibial nerve is elicited. The needle is withdrawn slightly and in the absence of any persistent paresthesia following negative aspiration, 8 cc of local is injected slowly. Tibial nerve block at the ankle is performed with the patient in the lateral position and the operative leg slightly flexed. In an aseptic fashion a 25 g 1.5 in. needle is inserted between the medial malleolus and the Achilles tendon toward the posterior tibial artery. After a depth of0.5-0.75 in., a paresthesia can be elicited. The needle is withdrawn about 1 mm and in the absence of persistent paresthesia and negative aspiration, a total of 6 ml of local is injected.

B. To perform this block, the patient is placed in the lateral position and the leg is flexed. A 25 g 0.5 in. needle is inserted at a point just below the fibular head and is advanced slowly toward the neck of the fibula until paresthesia is elicited. The needle is then withdrawn slightly, and local anesthetic solution is injected.

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